A particulate matter detection sensor of an electric resistance type is used to detect the amount of particulate matter (PM) in the exhaust gas discharged from an internal combustion engine. The particulate matter detection sensor has an insulating substrate and detection electrodes at least a part of which is embedded in the insulating substrate. The sensor includes a sensor element with a detection face, corresponding to an end face or a side face of the insulating substrate, at which the detection electrodes are exposed.
Over the detection face of such a sensor element, detection electrodes of different polarities are alternately disposed with an insulating layer interposed therebetween. An electrostatic field is formed by applying a voltage between these electrodes. As a result, the charged particulate matter is attracted to the electrostatic field and trapped on the detection face, thereby causing the electrodes to conduct. Thus, it is possible to detect the amount of the particulate matter contained in the exhaust gas based on the change in the resistance between the electrodes.
Typically, Pt electrodes are used as the detection electrodes. A sensor electrode of Pt or a Pt alloy for various sensors is disclosed in, for example, PTL 1. Further, PTL 2 discloses, as a detection electrode for a particulate matter detection sensor, an electrode made of Pt and a glass material having a softening temperature of 1000° C. or higher.